Method for controlling operation of a press

ABSTRACT

A method for controlling the operation of a press of the type including at least two mold parts arranged to be closed to define a mold cavity and opened relative to each other, relatively movable carrier plates each mounting a mold part, a toggle mechanism operable by a driving motor to displace one carrier plate relative to a stationary carrier plate, a joint plate engaged with toggle mechanism, beams extending between the stationary carrier plate and the joint plate, the beams constituting tension members interconnecting the stationary carrier plate and the joint plate, and a shifting mechanism for adjusting the effective length of the beams between the stationary carrier plate and the joint plate. The method of operating the press comprises setting a range of available driving power between minimum and maximum values, and during each cycle of operation measuring the peak driving power, comparing the measured power to the range of available power and responsive to the deviation of the measured power to the range of available power effecting or shifting of the beam length to restore the measured power to the range of available driving power.

June 25, 1974 EGGENBERGER ETAL 3,819,774

METHOD FOR CONTROLLING OPERATION OF A PRESS Original Filed May 5, 1969 4Sheets-5heet 1 l Illa "lb HI: I I s l" 5 52 53 -52 INVENTORS ULRKEA/BRGER BY IOSEF ZEIINDEI? ATTDRUEKS June 25, 1914 3,819,774

U. EGGENBERGER L METHOD FOR CONTROLLING OPERATION OF A PRESS OriginalFiled May a 1969 4 Shets-Sheet 2 Fig.2

INVENTORS ULRICH Essa/Barren dig- 56P 15 PER a rraR L/ Y:

June 25, 1974 U. EGGENBERGER ETAL METHOD FOR CONTROLLING OPERATION OF APRESS 4 sheets-sheet 3,

Original Filed May 5 1969 Fig.3

A TT'OR ME 75 Junc 1974 v u. EGGENBERGER ETAL 3,819,774

METHOD FOR CONTROLLING OPERATION OF A PRESS Original Filed May 5 1969 4sheets-sheet 4 Fig. v

INVENTORS uua/u/ aueweemssn :rasEF 2504/1251: BY

m mum i9 TWRNEYS Unie vS a s Patent 0131 9 METHOD FORCONTROLLINGOPERATION OF A PRESS Ulrich Eggenberger, Oberuzwil, and Josef Zehnder,

Niederuzwil, Switzerland, assignors to Gebruder Buhler AG, St. Gall,Switzerland Original application May 5, 1969, Ser. No. 821,822, nowPatent No. 3,642,405 Divided and this application Feb. 22,1971, S'er.No. 117,825 Claims priority, application Switzerland, May 9, 1968,

' Int. Cl. B29c 3/06 US. Cl. 264-40 6 Claims ABSTRACT OF THE DISCLOSUREA method for controlling the operation of a press of the type includingat least two mold parts arranged to be closed to define a mold cavityand opened relative to each other, relatively movable carrier plateseach mounting a mold part, a toggle mechanism operable by a drivingmotor to displace one carrier plate relative to a stationary carrierplate, a joint plate engaged with toggle mechanism, beams extendingbetween the stationary carrier plate and the joint plate, the beamsconstituting tension members interconnecting the stationary carrierplate and the joint plate, and a shifting mechanism for adjusting theeffective length of the beams between the stationary carrier plate andthe joint plate. The method of operating the press comprises setting arange of available driving power between minimumv and maximum values,and during each cycle of operation measuring the peak driving power,comparing the measured power to the range of available power andresponsive to the deviation of the measured power to the range ofavailable power effecting or shifting of the beamlength to restore themeasured power to the range of available driving power.

BACKGROUND OF THE INVENTION This is a division of application Ser. No.821,822, filed May 5, 1969, now U.S.Pat. 3,642,405.

During the operation of presses having at least two mold parts to beclosed, retained in closed position, and opened, it is frequentlydesirable to know the effectiveness of the mold closing, since theeffectiveness of the mold closing is responsible for the quality of theworkpiece produced by the press. This knowledge is very valuable,particularly in injection molding and in pressure casting machines,since it insures not only the quality of the workpiece but also thesafety of the machine, as well as preventing accidents to Operatingpersonnel. However, the operating parameters in these presses vary inthe course .of time, since thermal influences, originating from thematerial and from the cooling of the mold, respectively, are notconstant.

.gIt has already been proposed to check operating parameters, duringoperation of the press, and to correct them,

if necessary. One suggestion is to measure the stresses in the column orcolumns serving, on the one hand, to guide the mold parts and, ontheother hand, to transmit the mold closing forces which manifestthemselves as elongations of the columns, and to use these measuredvalues to make corrective adjustments to the mold closing device. Inthese proposals, known strain gauges are used, and these strain gaugesare secured on the stressed columns or guides. Alternatively, knownpiezoelectric gauges are arranged on the columns or guide anchor ties.In still another proposal, a gauge stick is arranged in a bore of thecolumn or guide to be measured.

The particular disadvantage of these measuring arrangements is that themeasured values, insofar as they are ob- 3,819,774 Patented June25, 1974SUMMARY OF THE I-NVENTION This invention relates to presses havingatleast two mold parts to be closed, retained in closed position, andopened and, more particularly, to a novel method of measuring variationsin the operating parameters of such presses, during operation thereof,and effecting corrective adjustments, during operation of the press,responsive to the measurements.

Tht objective of the invention is to eliminate the disadvantages ofknown prior art arrangements, and particularly to arrange measuringdevices on the press without weakening the columns or beams, withoutexpensive anchoring of those columns which are susceptible to trouble,and without the relatively easily vulnerable arrangement of themeasuring value recorders. Since it has been found, in addition, thatthe presently employed measuring methods, using the mentioned measuringelements determining the elongations of the columns, beams, or guides ofthe press, can be substantially simplified by a new atrangement ofmeasuring elements which determines different operating parameters ofthe press, the scope of the invention is directed to a wider goal than amethod for operating the press. Thus, the objective of the invention isto insure a constant closing power once it has been determined,independently of the frequently changing operating parameters, like heatinfluences, working speed, tool life, etc.

The method of the invention serves to operate a press having at leasttwo mold parts to be closed, retained in the closed position, and to beopened, and which are secured on oppositely moving respective moldcarrier plates, with the toggle mechanism and an associated drivingmotor arranged between one mole carrier plate and a joint plate andserving to displace the one mold carrier plate relative to the othermold carrier plate. The method is further applicable to such a pressincluding at least two stress absorbing beams connecting a fixed moldcarrier plate and the joint plate and extending laterally of theinterposed movable carrier plate, these beams being rigidly connectedwith the fixed mold carrier plate and with the joint plate by a shiftingdevice for adjusting the effective length of the beams between the jointplate and the fixed carrier plate. The characteristic feature of theinvention method is that, when the value of the driving power to beexpended by the driving motor for closing the mold exceeds a certainlimit or drops below a certain limit, or a range between an upper andlower limiting value, the shifting device is operated within a certainrange of movement of the oppositely moving mold carrier plates duringclosing of the molds, in order to vary the effective length of the beamsbetween the fixed. carrier plate and the joint plate.

In accordance with the invention, operation of the shifting device canbe effected within a constant distance. In addition, the shifting devicecan be driven in dependence on the difference between the measured valueof the driving power and a predetermined value or range of values.

The apparatus for performing the invention method, which is arranged onthe press as mentioned above, includes a dynamom'eter responsive to thedriving power which, when the predetermined value or value range betweenan upper and lower limiting value is attained, is provided in a powersupply line to the driving motor. At least one displacement path monitoris operatively associated with the toggle mechanism and the drivingmotorassociated with the toggle mechanism. The dynamometer and themonitor are connected in mutual func tional dependence into the controlcircuit of the shifting device.

In a press having a fluid pressure driving motor, a fluid pressurizingpump connected with the motor, and a fluid pressure operated switchacting as the dynamometer, the switch includes at least two switchingelements for corresponding switching operations associated,respectively, with an upper limiting value and a lower limiting value.

'In a corresponding arrangement for performing the invention method, thedynamometer can include elements for producing output valuescorresponding to the respective measured pressure, and which aresupplied to the control of the shifting mechanism. In further accordancewith the invention, comparisons between the theoretical values and theactual values of the pressure, during the predetermined displacementrange of the mold parts, are provided for influencing the shiftingmechanism.

An object of the invention is to provide an improved method of operatinga press of the type including at least two mold parts arranged to beclosed, to provide apparatus for performing the method.

A further object of the invention is to provide such a method in whichthe operating parameters of the press are continually measured and,responsive to the measurements, adjustments of the operating parametersare effected during operation of the press.

Another object of the invention is to provide such a method which arefree of the disadvantages of the prior art and in which measuringdevices are provided without weakening the beams or columns of thepress, expensive anchoring of the beams or columns, which aresusceptible to trouble, are obviated, and which operate without therelatively easily vunerable arrangement of measuring value recorders.

A further object of the invention is to provide such a method insuring aconstant closing power for the mold parts which, once it has beendetermined, is independent of the frequently changing operatingparameters such as heat influences, working speed, tool life, and thelike.

A further object of the invention is to provide such a method which maybe used in an injection molding machine or a pressure casting machinefor the production of injection molded plastic pieces or pressure castmetal pieces.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a graphic illustration of the path-force of a toggle jointpressure casting machine controlled in accordance with the invention;

FIG. 2 is a plan view of a pressure casting machine illustrating themost important elements thereof;

FIG. 3 is a schematic wiring diagram of a first embodiment of controlmeans for performing the invention method;

FIG. 4 is a schematic wiring diagram of a second embodiment of controlmeans for performing the method of invention; and

FIG. 5 is an elevation view, partly in section, illustrating theconnection of a nut, threaded on a beam, with a driving gear.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method forming the subjectmatter of the invention is illustrated in FIG. 1. FIG. 1 showsschematically, in its upper portion, the mold closing device with thetoggle joint mechanism and, in its lower portion, graphicallyillustrates various characteristic quantities In the strictly schematicrepresentation of a pressure casting machine in FIG. 1, a stationarymold carrier plate is illustrated at 1, a moving mold carrier plate at 2and a joint plate at 3, thesev plates being arranged along the forcetransmitting beams 4 and 4'. Stationary mold carrier platel carries moldpart 11, and movablemold carrier platez carries a second mold .part21..The toggle joint system 30 is interposed between'rnovable'moldcarrier plate 2 and joint plate 3," and is actuated by a drivingelement-or motor 31. A' shifting mechanism 50, operable to adjust thedistance between stationary moldcarrier plate 1 and joint plate 3, isillustrated schematically.

In the diagram, the displacement path of movable mold carrier plate 2toward stationary mold carrier plate 1 is designated S, while the moldclosing power necessary for its displacement is designated P The drivingpower of the mold closing device is designated P. i

The hyperbola P represents the-curve of the mold closing power, duringconstant utilization of the maximum available driving power P throughthe mold closing operation within the path extending from the abutmentof the mold parts 11 and 21, at S to the final closing of the mold atthe position 8,. The direction and the shape of the curve depend, to agreat extent, on the construction of the toggle joint mechanism. Themold closing power P which increases theoretically toward the'infinite,is limited, in the right part of the diagram, to a finite value due tovarious mechanical influences such as friction, deformation, braking,piston stroke, etc. The'power P of the driving motor is represented on adifferent and larger scale. 4

The line II illustrates the increase of the column or beam elongationwithout any additional elongation originating from other elements, as afunction of the mold closing path. More important, however, is thecharacteristic III which illustrates theincrease of the elongations andcontractions in theentire stressed' 'system, deformations in the jointsystem,-in the mold carrier plates, etc., being also taken intoconsideration, in addition to the elongations of the columns or beams.

Interest is centered mainly on the optimum operation of the machineduring the mold closing operation and the mold closure retainingoperation, using the available driving power. This means, primarily,that there'are no great reserves in the toggle joint mechanism withrespect to the rated capacity of the columns orbeams to withstandstress, but that this stress is primarily in the range of thepermissible material stress. This case exists when the applied moldclosing power just approaches the stress limits of the forcetransmitting elements which, in the present case, are the forcetransmitting beams4 and 4.

This stress is illustrated in FIG. 1 as occurring when thecharacteristic III is, at a point X, tangent to the curve P of the moldclosing power. In this path section S the entire or available drivingpower P is required to move the toggle joint system'30.' To the left andright of this utilization of the maximum driving power, the curve IV ofthe driving power drops relatively sharply, which suggests that there isa reserve between the available driving power and the required drivingpower, since curve IV is considerably below the maximum value Pdeterminant for one case.

In the path section S 'the mold parts 11 and 12 bear on one another and,from this time on, are forced increasingly against each'other. In thepath section S there is another saddle in curve IV sothat, at thispoint, there again exsists a considerable power reserve between theavailable driving power and the required driving power. From this pointon, the machine is stressed increasingly up to the maximumlocking power,the mold being finally closed in the path section 8, with the togglejoint system being brought nearlyinto the stretched dead centerposition. There is obtained for the given driving po'wer P that isachieved at the'end of' the closing operation,

the greatest possible'elongation of the force transmitting beams 4, 4,and the machine is thus best utilized.

It should be pointed out that this minimum value of curve P is actuallylower and displaced greatly to the right, compared to the representedcurve, which permits, however, distinguishing better between the variousload cases, due to a certain distortion. The second rise of curve P canbe accounted for by the fact that the theoretical curve P of the moldclosing power is no longer correct at this point, because it is, atfirst, reduced in time by a braking eifect with the element 31 at theend of the closing path, and because the driving element 31 abuts a stopso that the dead center of the toggle joint system 30 is not quitereached.

Deviation from this substantially optimum utilization of the machine inaccordance with the curves III and IV result from the curves IIIa, IIIband IIIc, as well as the curves IVa, IVb, and We. Because the values aretoo high in curves 111a and IVa, it can be seen that the mold can nolonger close, since the mold closing power resulting from the maximumavailable driving power can no longer effect an increase in the columnelongation because curve Illa intersects curve P in advance of the line8,. Within the path from S to S the maximum available power value Pwould be exceeded, as is illustrated by curve lVa.

This operation is extremely dangerous, since there is a risk or columnor beam rupture at the end of the mold closing movement, or at leastpermanent deformations of the columns can be expected, for example, by acareless increase of the maximum value P up to X in order to overcomethe column elongation.

However, if the machine is operated by the toggle joint system inaccordance with the curves IVb and IVc, and corresponding to the stresscharacteristics IIIb and 1110, the driving power within the displacementpath from S to S is below the minimum value P to be attained inaccordance to prediction, or even below a lower limiting value P Inthese ranges, the machine is operated rather uneoonomically, and thereis a great risk that the mold will burst open during the injection ofthe liquid plastic or fluid metal, so that the workpiece producedtherein will be defective and the sputtering hot material may causeserious injuries to operating personnel. This operating state,therefore, must be corrected by increased tension, that is, displacementof the joint plate 3 toward the stationary mold carrier plate 1 alongthe force transmitting beams 4 and 4.

It should be pointed out, however, that there are cases where the entireavailable mold closing power machine may not be used. For example, if amold originally designed for use in a smaller machine is used on alarger machine, the entire available mold closing power may not be used.In this case, too, the invention ofiers important advantages since itpermits controlling exactly the maximum admissible mold closing powerand by simple means.

The essential feature of the mold closing monitoring and correctingprocedures of the invention consists in determining the peak of the moldclosing power, appearing within a certain range of the mold closing pathat both sides, before the final closing of the mold, and to actcorrespondingly on the adjustment in either a tightening or a looseningsense. In other words, this means that a certain power of the drivingsystem actuating the toggle joint mechanism is determined within acertain displacement path of the toggle joint mechanism, and that acorrection is made, in case of deviations, in the distance responsiblefor it, between the stationary mold carrier plate and the joint plateconnected thereto by the beams, or in the spacing of the two moldcarrier plates with the dead center of the toggle joint mechanism inclosing position.

A first arrangement for performing the method of the invention isillustrated in FIGS. 2 and 3, in which a pressure casting machineincludes mold parts 11 and 12 secured on the respective mold carriers 1and 2. Beams 4 and 4' extend from mold carrier 1 through mold carrier 2to joint plate 3. Toggle joint mechanism is arranged between joint plate3 and mold carrier plate 2. Plate 3 carries a hydraulic cylinder 32 as adriving motor of the toggle mechanism 30, and a hydraulic pressuresupply arrangement 35 supplies motor 32 with power through a line 34 towhich is connected a dynamometer 33. Joint plate 3 also carries ashifting mechanism comprising a servo motor connected by gearing withnuts 61 mounted in joint plate 3 for rotation and relative displacementon the force transmitting beams 4 and 4'. A control cam 22 on a carrier24 is operatively associated with the joint head of toggle mechanism 30,and the machine base carries a displacement path monitor 8 comprisingthree limit switches 40, 41 and 43 which are operable by cam 42.Stationary mold carrier plate 1 is operatively associated with the moldcharging unit 5.

Displacement path monitor 8, comprising the limit switches 40, 41 and43, and dynamometer 33, are connected with step motor 50 in the gearing60 for the automatic determination of the operation of the machine andfor any correction of the distance between joint plate 3 and stationarymold carrier 1 arranged at opposite ends of the force transmitting beams4 and 4, and thus of the distance between the mold carrier plates 1 and2. They are connected together with additional elements to form acontrol device.

Referring more particularly to FIG. 3, a reversing switch 75, a relayfront contact r44, a relay back contact r61, and a double tap 81 of acommutator having two contact segments 82 and 83, are connected to asource of DC. potential through a conductor 71. From the contacts 01 ofreversing switch 75, a conductor 72 extends both to limit switch 43 andto contacts 411 of limit switch 41. The second contacts up of reversingswitch are connected by conductor 77 to contacts 401 of limit switch 40.The back contacts 431 of limit switch 43 are connected by conductor 73to the contacts 412 of limit switch 41, and a conductor 74 connectscontacts 412 commonly to contacts k1, k2, k4 and k6 of dynamometer 33. Aconductor 76 connects contacts 411 of limit switch 41 to front contactsk8 of dynamometer 33 which are operable to complete a circuit, from DC.potential source 70, to an alarm horn through a conductor 79. Horn 100is also connected to back contacts k1 of dynamometer 33, and is furtherconnected to a return line 99 leading to source 70.

The front contacts k2, k4 and k6 of dynamometer 33, which are commonlyconnected by conductor 74 to front contacts 412 of limit switch 41, areconnected individually, through respective conductors 92, 94 and 96, toreturn line 99. Conductors 92, 94 and 96 lead to respective relay coilsR R and R and are connected through associated front contacts r12, r22,r32 and a conductor 91 to the back contact r61, to serve as holdcircuits for the respective relays. A conductor 101 connects contacts401 of limit switch 40 to a thermal delay switch U having contactsconnected, respectively, to first terminals of relay coils R4 and R5whose second terminals are connected to return conductor 99. Frontcontacts I42 and r52 of relays R4 and R5, respectively, are connected toconductor 101 and are interconnected with each other to a series circuitincluding a front contact r14 of relay R1 and a back contact r23 ofrelay R2. A conductor 102 extends from contact r23 to one terminal of atightening solenoid M whose other terminal is connected to returnconductor 99. In parallel with conductor 102, a front contact r34 ofrelay R3 is connected, in the further power measuring circuit 96-99,into conductor 103 connected to one terminal of loosening solenoid Mwhose other terminal is connected to common return conductor 99.

A driving motor 85 for commutator 80 is energized through a frontcontact r44 of relay R4, which front contact is in series in a conductor105 leading from conductor 71, connected to D.C. potential source 70, toone terminal of motor 85. The opposite terminal of motor 85 is connectedthrough an adjustable speed controlling series resistance 86 to commonreturn conductor 99. A bridge 106 connects conductor 105 to the innercommutator strip 82, and is also connected to the movable contact ofreversing switch 90 for tightening and loosening of the adjusting nuts.Respective conductors 52 and 53 connect the reversing switch contacts rand r to servo motor 50 of the shifting mechanism, which servo motor isalso connected to common return conductor 99. The outer commutatorsegment or strip 83 is very short and, between it and common returnconductor 99, there is connected a relay coil R6 which operates the backcontacts 161. A reversing switch 55 is connected between conductors 52and 53 and conductor 101 which leads to the contacts 401 of limit switch40. Reversing switch 55 is normally in its center or off position.

The operation of the arrangement shown in FIG. 3 will now be described.Assuming that initially D.C. potential source 70 is disconnected, allthe components of the circuit are in the represented positions. WhenD.C. potential source 70 is connected, potential is applied to a circuitincluding contacts p of reversing switch 75, conductor 77, contacts 401of limit switch 40, conductor 101, thermal lag switch U and relay R4.Relay R4 is thus transferred so that front contacts r42 and r44 areclosed and driving motor 85 of commutator 80 is thus immediatelyenergized. Motor 85 begins to rotate with a fixed speed determined bythe adjustment of resistance 86. Tap 81 of commutator 80 engages innercommutator segment 82, but such engagement does not affect either thefurther course of the rotation of motor 85 nor any operation of shiftingmechanism 50-60.

After a certain time interval, thermal lag switch U has been heatedsufiiciently that it opens the connection to relay R4 and closes theconnection to relay R5. Thus, front contacts r42 and r44 are opened, andfront contacts r52 of relay R5 are closed. However, since front contactsr14 and r34 are open, this operation has no further effect. Frontcontacts r44, which are now open, also have no influence, because motor85 continues to run as it is supplied with current through innercommutator segment 82 and bridge 106. When tap 81 engages outercommutator segment 83, relay R6 is energized briefiy and back contactr61 is opened. After a further short rotation of driving motor 85,double tap 81 disengages both commutator segments 82 and 83, motor 85 isdeenergized and back contact r61 or relay R6 is re-closed. Only thermaldelay switch U remains in its new position and maintains relay R5energized so that front contacts R52 also remain closed. However, thishas no further effect.

If reversing switch 75 is switched from its opened position 0p into itsclosed position 01, which occurs upon the starting signal formold-closing movement from the machine control (not shown), thermaldelay switch U is deenergized and, after a cooling period, returns toits represented back position. Due to the displacement of mold carrierplate 2, and thus of control cam 22, contacts 401 of limit switch 40 areopened. During movement of mold carrier plate 2 through the distancefrom the fully opened position of the mold to the reversing switch 41,which movement corresponds substantially to the switching path to pointS of FIG. 1, nothing happens in the control.

When the operation proceeds past point S limit switch 41 is reversed toopen its contacts 411 and close its contacts 412. Thereby, conductor 74is connected to the D.C. potential source 70 and conductor 76 isdisconnected therefrom. At the point S the pressure in dynamometer 33begins to increase. Even before the operation reaches point S themovable element of the dynamometer should be moved from its restposition to open the contacts k1, in normal operation. However, if thisdoes not occur, the machine is set completely wrong,

and alarm horn 100 is energized over the circuit now extending from D.C.potential source through the circuit including conductor 71, contacts 01of reversing switch 75, contacts 431 of limit switch 43, contacts 412 oflimit switch 41, conductor 74 and contacts k1, as well as the conductor79 and 99 forming the return to D.C. potential source 70. Alarm horn 100warns that a readjustment of the machine is necessary.

In the normal operation of the machine, which is operation with acorrect setting, the back contacts k1 of dynamometer 33 have openedbefore limit switch 41 is actuated by control cam 22 so that, when limitswitch 41 is reversed, alarm horn 100 can no longer be energized. If thepressure in the pressure gauge constituting the dynamometer 33 attains avalue which is either greater than or equal to P but less than P duringmovement of cam 22 from limit switch 41 to limit switch 43, whichcorresponds to movement from path section S to path section 5;, of FIG.1, the two front contacts k2 and k4 of dynamometer 33 are closed whilethe other two front contacts k6 and k8 remain open. Relay coils R1 andR2 are thus energized and immediately held through their associatedfront contacts r12 and r22, as well as through the back contacts r61 ofrelay R6.

When control cam 22 passes by limit switch 43, the back contacts 431 ofthis switch are opened and the mold parts 11 and 12 are in the closedposition. Although the current supply to relay coils R1 and R2 throughlimit switches 41 and 43 is now interrupted, these two relays remainenergized through the respective self-holding front contacts r12 andr22. Opening of limit switch 43 now permits dynamometer 33 to rise abovethe tolerance range and thus to energize the alarm horn 100 throughcontacts k8 without any effect on front contacts k6. This is the casewhen the maximum mold closing power P has been attained.

By switching reversing switch from contacts c1 to contacts 0p for themold opening movement, which switching coincides normally with thesignal from the machine control or is provided by the latter, moldcarrier plate 2 moves away from stationary mold carrier plate 1, moldparts 11 and 12 are opened, and ejection of the finished workpiece ispermitted. The pressure in the pressure gauge constituting dynamometer33 collapses, and front contacts k6, k4 and k2 are opened again and backcontacts k1 are closed.

When the limit switch 40 is reached by cam 22, switch 40 is operated toclose its contacts 401. Relay R4 is energized immediately throughthermal delay switch U and the two front contacts 142 and r44 areclosed. Motor 85 of commutator 80 again begins to run. Due toenergization of relays R1 and R2, which are still self-held, frontcontacts r14 remain closed and back contacts r24 remain open, so thattightening magnet M is not energized. However, since relay R3 alsoremains deenergized, its two front contacts r32 and r34 are open andloosening magnet M also is unenergized so that reversing switch 90remains in its center position.

When double tap 81 engages commutator segment 82, motor 85 of commutator80 has its energizing circuit held closed through bridge 106- so thatthe motor 85 continues to operate. In the meantime, thermal switch, Uswitches into the position energizing relay R5, which results in openingof front contacts r42 and r44 of relay R4, as well as in closing offront contacts r52. This has no effect on the other functions in thisoperation. Due solely to the holding circuit closed through innercommutator segment 82, motor 85 continues to run until tap 81 disengagescommutator 82, and the motor is then deenergized. Shortly beforestopping of the motor, relay R6 is instantaneously energized and backcontacts r61 open to break the holding circuit for relays R1 and R2.Thus, the control device is again in a starting position.

If, between actuation of limit switches 41 and 43 during a mold closingoperation, only the back contacts k1 of dynamometer 3-3'0pen and onlyfront contacts k2 close, so that only relay R1 is energized so that itsfront contactsr12 and r14 are closed, tightening solenoid M of reversingswitch 90 is energized, after the mold 11-21 has opened, over a newlyestablished energizing circuit. This circuit extends from DC. potentialsource 70 through reversing switch 75, contacts 401 of limit switch 40,conductor 101, thermal delay switch U relay winding R4 and returnconductor 99. Relay R4 closes its front contacts r42 and r44. Tighteningsolenoid M is then energized through closed front contacts r42 and r14,closed back contacts r23 and conductor 102. Reversing switch 90 thuscloses its contacts r Simultaneously, motor '85 begins to turncommutator tap 80, motor 85 being energized through the closed frontcontacts r44.

Servo motor 50 of the shifting mechanism is energized through bridge106, reversing switch 90 and conductor '52, so that joint plate 3 ismoved along beams 4 and 4', connected to stationary mold carrier plate1, through the gear connection 60 and the nuts 61. After thermal delayswitch U has been reversed, the front contacts r42 and r44 of relay R4are opened, and front contacts r52 of relay R5 are closed, so that theenergizing circuit for solenoid M of reversing switch 90 remains closed.Motor 85, which is energized over bridge 106, operates commutator80,-When tap 81 engages outer commutator segment 83 of commutator 80,relay R6 is energized and back contacts r61 are opened, and thus theholding circuit of relay R1 is interrupted. Relay R1 therefore opens itsfront contacts r12 and r14, which effects deenergization of tighteningsolenoid M so that reversing switch 90 returns into its center positionand interrupts energization of shifting mechanism 50. When tap 8 1 ofcommutator 80 has disengaged both commutator segments 82 and 83, theholding circuit of motor 85 is interrupted and motor 85 stops. Thermaldelay switch U remains, due to its heating, in its position.

However, when the driving power attains the value P within the pathsection 8 -8 by actuating the toggle mechanism for closing the mold, thefirst three front contacts k2, k4, and k6 of dynamometer 33 are closed.The other functional steps of limit switches 40, 41 and 43, as well asof thermal delay switch U remain the same. In addition, all three relaysR1, R2 and R3 are energized and remain energized through the holdingcircuits closed by the respective contacts r12, r22 and r32. Therespective front contacts r14 and r34 of relays R1 and R3 are thusclosed, and the back contacts r23 of relay R2 are opened.

With the mold open again, and the press receiving the signal for openingthe mold, in this operating state, automatically from the machinecontrol and preferably on the basis of the dynamometer result, that is,over an additional front contact of relay R3 acting on the machinecontrol, limit switch 40 is reclosed so that relay R4, having frontcontacts r42 and r44, is energized through thermal delay switch U Frontcontacts r42 and r44 are closed, and-a circuit is completed throughclosed front contacts r34 to loosening solenoid M to energize the latterand switch reversing switch 90 to close its contacts r Shiftingmechanism 50-60 begins to run. Driving motor '8 5 of commutator 80 isalso energized and closes a holding circuit through tap 81, commutatorsegment 82 and bridge 106.

During delayed switching of thermal delay switch U relay R5 is energizedinstead of relay R4, and thus the circuit is changed from front contactsr42 to front contacts r52, the current supply to driving motor 85 ofcommutator 80 is opened at front contacts r44, and is maintained onlythrough the holding circuit. As long as tap 81 engages segment 82 ofcommutator 80, which can be determined by adjusting resistance 86,shifting mechanism 50-60 shifts the position of joint plate 3 away fromstationary mold carrier plate 1. After one revolution of tap 81 ofcommutator 80, all the relays R1-R3 are deenergized, and shiftingmechanism 50 and motor 85 of commutator 80 are also deenergized.However, current continues to flow from back contacts 401 of limitswitch 40 through the thermal contact of delay switch U to relay R5,whose front contacts r52 remain closed.

It should be pointed out at this time that the frequency of theloosening steps is limited by a suitable circuit, for example, acounting circuit. This is due to the possibility that after a castingedge has been formed and has not been removed from the workpiece, anexcessive mold closing power is indicated erroneously by the dynamometerduring the next mold closing, because of this casting edge clampedbetween the two mold parts. Consequently, the mold is opened, theshifting device is operated in a loosening direction and the mold isreclosed, this time prestressed in the desired range. However, becauseof the gap that now exists, in practice, between the mold parts, andwhich is due to the casting edge, additional casting material will enterthis gap during the next charge, and probably will not be removed duringthe next ejection of the workpiece, particularly because of the growthon the older casting edge. With repeated corrections of the mold closingunit, the operating personnel is in very great danger. Therefore, thenumber of substantially successive loosening steps must be limited and,when this limiting value is attained, an alarm must be sounded, thepress must be stopped, or both. The starting position for this countingis the start of the operation of the press signal to the control ascorrect, for example, by a signal operation automatic following thesignal setting automatic.

If joint plate 3- should be too close to stationary mold carrier plate1, for some reason, and thus the mold closing pressure exceed themaximum value P before cam 22 reaches limit switch 41, that is, beforethe movement reaches the path section S of FIG. 1, alarm horn will beenergized due to the connection from reversing switch 75 through backcontacts 411 of limit switch 41 and the front contacts k8 of dynamometer33 which latter have already been closed by the excess pressure. Thepress must be opened immediately, which is likewise advantaegouslyeffected automatically by the machine control. In this case, it isnecessary that the shifting can also be effected manually andindependent of the automatic shifting.

For this purpose, reversing switch 55 is connected between conductor101, extending from limit switch 40, and conductors 52 and 53 leading toshifting mechanism 50-60. It is only when the mold is opened that it ispossible to loosen the mold tension, by throwing reversing switch 55 tothe right, or to increase the tension on the beams, by turning reversingswitch '55 to the left.

Despite the relatively simple construction of the control device, it ispossible, due to the effective operation of the press, to keep thelatter in the optimum working range and thus to eliminate the risk ofdefective pieces to a great extent. In this embodiment of the control,the description was started from the consideration that each correctionis effected step-by-step by a certain fixed amount. Even though thecontrol is effected with electromechanical elements, such as relays,thermal delay switches, reversing switch, etc., it is logical, in thepresent state of technology, to replace the latter, if necessary, by astrictly electronic, transistorized control device, or other deviceprovided with stationary logic elements.

In certain cases, it may be advisable to effect any shift, forcorrecting the position of joint plate 3, and thus for correcting themold closing power to be expended, in direct dependence on the actualvalue deviation from a given theoretical value, that is, toeffect thecorrection not by a certain amount, but by a quantity associated withthe deviation. A control device for effecting this is illustrated inFIG. 4.

Referring to FIG. 4, limit switches 40, 41 and 43, as well as reversingswitches and 75, connected to a source of D.C. potential, are stillused. In addition, a tightening solenoid M and a loosening solenoid Mwith the associated reversing switch 90, are connected to potentialsource 70, indicated in FIG. 4 as G. Conductors 52 and 53 extend fromthe respective contacts r and r of reversing switch to shiftingmechanism 50-60, which is also connected to common return line 99.Dynamometer 33 is provided with a double tap '121 and with a circuitclosure 122. Tap 121 is provided for establishing a connection betweentwo contacts 121a and 121b, on the one hand, and for determining acertain resistance value along a measuring resistance 120. Tap 121, whenengaged with measuring resistance 120, is also engaged slidingly with anelongated contact strip 125. Closure 122 of dynamometer 33 serves, incertain cases, to close contacts r122 in conductor 76 connected to thecontacts 411 of limit switch 41, for energizing alarm horn which latteris also connected to contact 121b. The second contact 121a is connectedto measuring point resistor and also to front contacts 412 of limitswitch 41.

In order to determine the theoretical value, a reference resistor 130,comprising a resistance wire, an adjustable tap 131 and an elongatedcontact 153, is provided. Reference resistor can be adjusted to acertain value, and the resistance wires of measuring point resistor 120and reference resistor 130 are connected in parallel. A relay R10, withreversible contacts 103 and 105, is connected with front contacts 401 oflimit switch 40 through a conductor 101. The transfer contacts r103 andr105 of relay R10 are connected, on the one hand, to contact strip andto contact strip 125 and, on the other hand, to a measuring and settingdevice 129 responding to the maximum values of the applied voltages. Therest contacts 103 and 105 of relay R10 are connected to contacts 145 and146, respectively, in a first commutator having two maximum pointers 141and 142, and are also connected with the commutator segments 153 and154, respectively, of a second commutator 150 having its shaft in commonwith that of commutator 140. 'In addition, these rest contacts areconnected to each other through a return motor 139 which is in serieswith an adjustable speed setting resistor 138.

The common shaft 155 of the two commutators has fixed thereto the rotorof return motor 139, the maximum pointers 141 and 142, and the tap 151.Maximum pointers 141 and 142 of first commutator 140, which are designedas taps, are connected with common return line 99 leading to dopotential source G. Tap 151 of second commutator 150 is connected toconductor 101 extending from limit switch 40 to relay coil R10. Thecommutator segments 143 and 144 of first commutator 140 are individuallyconnected, by respective conductors 148 and149, with tightening solenoidM5? and loosening solenoid M respectively, of reversing switch 90.

The control device shown in FIG. 4, for operating a toggle joint press,permits a procedure which will now be described. Movement of reversingswitch 75 from the opened position 0p into the closed position c1,occurring at the start of the mold closing movement, and the subsequentactuation of limit switches 40, 41 and 43, takes place exactly asdescribed above. Initially, standard resistance 130 is set, byadjustable tap 131, to a predetermined theoretical value. Withcontinuing mold closing movement, dynamometer 33 and tap 121 thereof aremoved to the left. In normal operation of the press, tap 121 ofdynamometer 33 is moved, into a corresponding position, in the rangebetween path positions S and S that is, between actuation of limitswitch 41 and actuation of limit switch 43, corresponding to the settingof reference'resistance 130. Consequently, there is no voltagedifference between taps 121 and 131, device 129 indicating the peakvalue remains in the rest position, and the associated maximum pointers141 and 142, of commutator 140, and tap 151, of commutator 150, are notmoved.

When the mold is reopened, there are no currents flowing from maximumpointers 141 or 142 through the associated commutator segments 143 or144, respectively, and no current flows to return motor 139. This latterhas been connected, by reversing switches 1103 and r105 switched bylimit switch 40 which energizes relay R10. Furthermore, no current fiowsto tightening solenoid Msp or to loosening solenoid M Shifting mechanism50, which is connected by gearing 60 with adjusting nuts 61 on jointplate 3, is not actuated. 1 I

However, if tap 121 of dynamometer 33 is brought into a positiondiffering from the position of tap 131 of reference resistance 130,a'voltage difference exists between resistors 120 and 130. Measuring andsetting device 129 is shifted into a corresponding position, and one ofthe maximum pointers 141, 142 of first commutator 140, as well as tap151 of second commutator 150, is moved to engage the correspondingcommutator segments 143 and 153, or 144 and 154, respectively. Duringopening of the mold, taps 141 or 142 and tap 151 remain in the positionsattained thereby. In addition, the tap 141 or 142 which is not movedremains in contact with contact-145 or 146, as the case may be. a

With the closing of limit switch 40 in the opened position of the press,relay R10, having the reversing contacts r103 and 1105- is energized. Acurrent thus flows from conductor 101, on the one hand, through tap 151of second commutator and one commutator segment 153 or 154, opposite tothe measuring direction, and through return motor 139 and seriesresistance 138, so that return motor 139 is actuated in a correctingsense as long as there is contact between tap 51 and the respectivecommutator segment 153 or 154. In parallel with this circuit, a currentflows from conductor 71 through one of the solenoids M or M to theassociated commutator segment 143 or 144 of first commutator 140, fromwhich. the circuit is closed over the associated tap 141 or 142 to thecommon return line 99. 1

This excitation of one of the tightening or loosening solenoids M or Mmaintains reversing switch 90 closed in one of the two positions r orr;,, respectively. The shifting mechanism thus is actuated in either anopening or a closing sense by the circuit G-7l-90-52 or 53-50-99-G,respectively. At the moment when a tap 141 or 142, and tap 151, aremoved back into the zero position and thus are no longer in engagementwith commutator segments 143 and 153 or 144 and 154, the respectivetightening or loosening solenoid M or M is deenergized, reversing switch90 is returned to the central neutral position, shifting mechanism 50-60is deenergized'and return motor 139 is deenergized.

If the range of dynamometer 33 within the determined path section S to SofFIG. 1, which is controlled by limit switches 41 and 43 and whicheffects the automatic tightening or loosening of the toggle jointsystem, is either not reached or is exceeded, contacts 121a and 12112remain interconnected by tap 121, or contacts 122 are closed by contactclosure 122, which results immediately in energization of alarm horn 100to provide a signal. In order to correct such a wrong setting, amanually operated reversing switch 55, which is normally in a centralneutral position is provided to connect conductors 71 go conductors 52and 53 leading to shifting mechanism The design of the control device asshown in FIG. 4 permits, at all times, correction of the mold closingpower by the necessary amount. That is, a wrong setting or a change inthe operation of the press is always effected by a single correction andback into the theoretical range. In contrast to the first embodiment ofFIG. 3, this rep resents, in most cases, an acceleration of thecorrection, since the press does not open and close several times untilit is set in the desired range. i

In order to shift joint plate 3, and thus the entire toggle jointmechanism 30 with the mold carrier 32 connected'thereto, it is knowntoprovide nuts 61 supported in joint plate 3, these nuts beingdisplaceable by rotation on threaded portions 204 of beams such as 4. Itis also known to drive several nuts 61, arranged on several beams 4, 4'and 4", by a common driving element connected by gearing to the nut forexample, a servo motor 50, a hydro motor, etc., which is'driven by alarge gear (not shown) which is in engagement with all the drivenelements, or by common driven worms engaged with worm gears (also notshown). In view of the fact that the mold, comprising the mold parts 11and 21, frequently must be secured unilaterally on the mold carrierplates 1 and 2, it is necessary to vary the positions of nuts 61 on thevarious beams 4, 4 and 4". This requires special devices in thetransmission from the central driving system 50-60 to the individualnuts 61.

An advantageous arrangement for efi'ecting this is shown in FIG. 5, inwhich each beam 4 is displaceably threaded through a respective nut 61.A first substantially cylindrical section 206 of each nut 61 is formedwith a groove, or with a plurality of slots, 207 for receiving the hookof hooked wrenches. Adjoining cylindrical section 206, each nut has ashoulder 208 against which there abuts a ring gear 210 having teeth 211.In order to tighten ring gear 210 with nuts 61, two annular clampingelements 215 and 216 are arranged on cylindrical section 206, theseelements having oppositely directed wedge cross sections whose slopingsurfaces bear against each other. A clamping ring 219 is provided fortightening annular clamping elements 215, 216, and is drawn toward ringgear 210 by screws 220 threaded into ring gear 210. Tightening of screws220 results in a distortion of clamping elements 215, 216 and thus in apositive coupling of ring gear 210 with nuts 61 on cylindrical section206.

Nut 61 is rotatably mounted, while being held against axialdisplacement, by means of an additional shoulder 218 and two thrustbearings 222 and 224, one interposed between nut 61 and joint plate 3and the other between shoulder 218' and a shouldered ring 225 pushedover nut 61 and connected by at least one screw 226 with joint plate 3.Along the circumference of nut 61 and overlapping thrust bearing 224engaging joint plate 3, there is provided a scale 230. Joint plate 3carries a pointer 231 directed toward scale 230. Ring 225 is cut out atthe position of pointer 231 to form a window 232 in such a way that apart of scale 230 is visible from the exterior.

Due to the arrangement shown in FIG. 5, it is possible always to keepring gear 210 in mesh with the common driving element 62. For individualadjustment of the nuts 61, it is necessary only to loosen clampingscrews 220, and thus clamping ring 219, so that the clamping elements215 and 216 are also loosened. Subsequently, joint plate 3 can bedisplaced through a certain distance, in either a tightening orloosening sense, on thread 204 of its beam 4. by engaging a hookedwrench with one of the slots or grooves 207 in nut 61 and rotating thenut in the appro priate direction. The extent of rotation of the nut 61can be read at any time on scale 230 opposite pointer 231. In case it isnecessary again, after such a unilateral tightening of one or all beams4, to tighten all beams 4, 4' and 4" equally, this no longer has to bedone experimentally. By virtue of scale 230, itis readily possible, inview of the fact that a unilateral tightening never exceeds one completerevolution of a nut 61, to bring all the nuts into the same scaleposition with respect to pointer 231.

The construction of the device is very simple, the connection from thedriven ring gear 210 to the nut 61 to be driven is extremely strong andyet easily disengageable, and the turning back from dilferent nutpositions on the beams to the same positions is always possible in asimple and accurate manner.

1 It will be clear that various modifications can be made with respectto the controls for the automatic shifting of the mold closing power asrepresented, for example, in FIGS. 3 and 4, without departingessentially from the spirit of the invention. As mentioned above, anyelectrical or mechanical control can be transformed logically into anequivalent electronic control. The same holds true for thetransformation of an electrical control into a pneumatic or hydrauliccontrol. In addition, it is not absolutely necessary to use limitswitches to monitor the displacement. Equivalent, or in certain cases,even superior, monitoring devices can be used for this purpose, such aslight barriers, electro-capacitative or electro-inductive devices, or,instead of electrical path monitoring elements, there can be usedhydraulic, pneumatic or mechanical monitor ing elements.

The shifting mechanism can consist, as mentioned above, of a chain gear,a gear drive, or a combination of both. Separate drives also can beprovided for the individual nuts, and it is merely necessary toascertain that synchronous shifting of all nuts to be driven is assured,which can be effected, in the case of electric motors, by electricsignals, and in the case of hydraulic or pneumatic devices, by knownpressure and flow rate systems.

The means connecting the ring gear with the nut can also be arranged asseveral pairs of ring clamping elements or a three-part ring clampingelement, for example, where a clamping ring with sloping surfaces onboth sides, in an axial direction, and clamping rings with slopingsurfaces on only one side, arranged at both sides thereof, is used.

What is claimed is:

1. The method of operating a press, of the type including at least twomold parts arranged to be closed, to define a mold cavity, and openedrelative to each other, relatively movable carrier plates each mountinga mold part, a toggle mechanism operable by a driving motor, having amaximum available driving power, to displace one carrier plate relativeto a second carrier plate, a joint plate engaged with the togglemechanism, beams extending on both sides of one carrier plate betweenthe second carrier plate and the joint plate, and laterally of thecarrier plate, the beams constituting tension members interconnectingthe second carrier plate and the joint plate, and a shifting mechanismfor adjusting the effective length of the beams between the secondcarrier plate and the joint plate: said method comprising the steps ofsetting a minimum peak driving power, less than said maximum availabledriving power, to be attained during closure of the mold, to establish adriving power range Whose upper limit is said maximum available drivingpower and whose lower limit is said minimum peak driving power; duringeach cycle of opening and closing the mold, initiating closure of themold with the mold parts moving along a closing path and with the beamshaving a preset length normally effective to assure complete closure ofthe mold parts; during the same closure of the mold, measuring the peakrequired driving power in a certain range of the closing path, inadvance of the final closing of the mold and after the mold parts are incontact with each other; responsive to such measured peak requireddriving power being less than such driving power range, operating theshifting mechanism, during the same cycle, in a direction to re ducesuch effective length of the beams to increase the measured peakrequired power to a value within such driving power range; and,responsive to such measured peak required driving power exceeding suchdriving power range, operating the shifting mechanism, during the samecycle, in a direction to increase such effective length of the beams todecrease the measured peak required power toward such driving powerrange.

2. The method of operating a press, as claimed in claim 1, in which themagnitude of the adjustment in such efiective length of the beams bysaid shifting mechanism is equal to the dilference between such measuredpeak required driving power and the mean value of such driving powerrange.

3. The method of operating a press, as claimed in claim 1, includingconverting any deviation of such measured peak required driving powerfrom such driving power range into a shifting signal; and utilizing theshifting signal to energize the shift mechanism to adjust such efi'ec:tive length of the beams in a direction to correct such deviation. V p

4. The method of operating a press, as claimed in claim 3, includingcontrolling the energization of the shifting means by the shiftingsignal to limit the resulting adjustment of the measured peak requireddriving powerto a value not greater than such driving power range; and,responsive to the measured peak require driving power attaining a valueequal to the upper limit of such driving power range before the mold isclosed, interrupting closing of the mold.

5. A method, as claimed in claim 1, in which the press is an injectionmolding machine for producing injection molded plastic workpieces.

1,6 6. A method, as claimed in iclairni 1, jn which the press is a diecasting machine'for producing-pg; surefgcametal workpieces.

u References Cit A Y; .w YUP T QQ A esaw s 3,579,741 '5/19711 13,423,502; .lzr9s9 I 1 .3,628,6l 12/1 9* 21 398 9/1941;

. a 3{; 1.9 ROBERT i wn lrili iiiiary grain i e T. P. PAVELKKQ'AssistanrExaminer

